The Thomas Jefferson Memorial is an iconic monument that is widely identifiable both throughout the United States and the world. Located within National Mall and Memorial Parks, a unit of the National Park Service in Washington, DC, the design of this white marble monument combines classical iconography with modern construction to enshrine the ideals associated with one of this country’s founding fathers. Over the last decade, Memorial has become rapidly soiled by biofilm. The blackening effect of biofilm, a colony of microscopic organisms that adheres to stone surfaces, was first noticeable in discrete areas of the memorial’s white marble in 2006, and has become more pronounced in recent years. While it manifests itself in various ways, the biofilm is most pervasive—and most visible—on the Memorial’s dome. A multi-disciplinary team of conservators, architects and other professionals has been studying the growth on the Jefferson Memorial since 2014 to determine the best treatment options. After careful review, it was decided that the initial cleaning test would be performed using laser ablation. Laser ablation offers maximum protection to this significant cultural resource as well as the surrounding natural resources: by fine-tuning the laser settings to the specific stone and soiling types, laser operators can remove the biofilm without damaging historically sensitive marble. The use of laser is also an environmentally sound procedure and eliminates the need to use more aggressive chemicals or abrasive cleaning methods. Rigorous safety controls are maintained for the duration of the cleaning process to protect the public and the operators. The project will achieve the cleaning of a test area of 1,000 square feet on the northeast side of the Memorial. This presentation will evaluate the efficacy of laser cleaning to remove biofilm through the lens of this trial cleaning effort. This will include a discussion of: the decision process by which this cleaning method was arrived upon; the characterization and understanding of this biofilm phenomenon to date; the intricacies of implementing and scaling a cleaning project at this site; and what might be done to prevent or deter soiling recurrence in the future. A brief comparison of this phenomenon to the incidence of biofilm at other major sites in Washington, DC will also be included.

Ms. Bello is Architectural Conservator for National Mall and Memorial Parks, a unit of the National Park Service (NPS) in Washington, DC. Her primary responsibility is overseeing the ongoing conservation of the major public art collection of statues, monuments, Memorials, and fountains... Read More →